This application claims the priority of German patent document 196 45 389.5, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for regulating the full-load injection quantity of a diesel internal combustion engine.
German patent document DE-A-26 50 247 describes a method for limiting the maximum permissible fuel feel quantity of a diesel engine fuel pump equipped with a mechanical speed governor. In this case, for optimum utilization of engine power, a limited full-load feed quantity assigned to the respective engine speed is derived from a full-load feed quantity characteristic map. The air mass supplied to the engine serves as a second operating variable in addition to the engine speed. For supercharged diesel engines, the charge-air pressure is used as a second operating variable.
By virtue of the method described there, the engine is utilized up to the power limit even in the transient mode (which, in the case of internal combustion engines, represents the transition from a low load state to a higher load state), and the most favorable acceleration values can thereby be achieved.
This transient mode is subsequently followed by a uniform steady-state mode.
However, the measures taken in this method are highly complicated and, furthermore, cannot fully achieve their object of the optimum utilization of the diesel engine in the transient mode.
U.S. Pat. No. 4,655,186 discloses a method for controlling the injection quantity of an Otto internal combustion engine so as to avoid an excessively lean mixture under a high load. In Otto engines, the mixture becomes leaner as a physical consequence of the transient state which prevails during acceleration from a low load. When the mixture becomes leaner, the exhaust-gas temperature rises, which under some circumstances may damage the exhaust-gas catalyst.
According to the method described there, a larger quantity of fuel and therefore an over-enriched mixture is injected as a countermeasure to the mixture becoming leaner. The method can be used only in an Otto engine, since, in a diesel engine, different preconditions prevail with regard to thermodynamic equilibrium of the internal combustion engine. Furthermore, such method can be used only within very narrow limits, since ignitability is no longer ensured if the mixture is too highly enriched. Only a very slight power or torque increase (for better acceleration) can be achieved by means of the method described there.
German patent document DE 37 00 401 C2 describes a mixture-regulating device for the feedback regulation of the air/fuel ratio of an internal combustion engine which is normally operated with a lean mixture. In order to achieve a desired response behaviour, along with a low emission of No.sub.x, even in transient states of the internal combustion engine, a control is provided such that the change in the air/fuel ratio temporarily exceeds an amount necessitated by the change in a desired value. Complicated mechanical devices are required for this purpose, however; and, they do not allow accurate control. Furthermore, a torque increase or power increase cannot be achieved by means of the device described there.
The object of the invention is to provide a method which improves the driving dynamics of a diesel internal combustion engine by simple means, without the need for accessories.
This object is achieved by the method according to the invention, in which operation of the diesel internal combustion engine is divided into three phases. Gas acceptance as well as torque, and consequently also driving dynamics in the transient mode, are considerably improved by adding an extra fuel quantity, which is supplied to the diesel internal combustion engine during the latter portion of the first phase and in the second phase. In the third phase a steady state level is maintained. This improvement is expressed, in particular, in shorter acceleration times, even from low engine speeds.
It is advantageous, furthermore, that no accessories are required in order to carry out the method according to the invention and it can therefore be carried out in a simple way.
In diesel engines, the combustion-space temperature depends on the load state of the engine. Consequently, at low load, such as, for example, during idling, the combustion-space walls are relatively cold. The time-limited extra quantity is possible only because the combustion-space walls of the diesel internal combustion engine are cold under low load. If the combustion-space walls were warm or hot, as they are when the engine is in the highly loaded state, the extra quantity would cause the critical temperature of the combustion-space walls to be exceeded. The method according to the invention is therefore used solely for acceleration from a no-load or low-load state or in a transient mode.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.